Getting types of the attributes in an ActiveRecord object
-
25-09-2019 - |
Question
I would like to know if it is possible to get the types (as known by AR - eg in the migration script and database) programmatically (I know the data exists in there somewhere).
For example, I can deal with all the attribute names:
ar.attribute_names.each { |name| puts name }
.attributes just returns a mapping of the names to their current values (eg no type info if the field isn't set).
Some places I have seen it with the type information:
in script/console, type the name of an AR entity:
>> Driver
=> Driver(id: integer, name: string, created_at: datetime, updated_at: datetime)
So clearly it knows the types. Also, there is .column_for_attribute, which takes an attr name and returns a column object - which has the type buried in the underlying database column object, but it doesn't appear to be a clean way to get it.
I would also be interested in if there is a way that is friendly for the new "ActiveModel" that is coming (rails3) and is decoupled from database specifics (but perhaps type info will not be part of it, I can't seem to find out if it is).
Thanks.
Solution
In Rails 3, for your model "Driver", you want Driver.columns_hash
.
Driver.columns_hash["name"].type #returns :string
If you want to iterate through them, you'd do something like this:
Driver.columns_hash.each {|k,v| puts "#{k} => #{v.type}"}
which will output the following:
id => integer
name => string
created_at => datetime
updated_at => datetime
OTHER TIPS
You can access the types of the columns by doing this:
#script/console
Driver.columns.each {|c| puts c.type}
If you want to get a list of all column types in a particular Model, you could do:
Driver.columns.map(&:type) #gets them all
Driver.columns.map(&:type).uniq #gets the unique ones
In Rails 5, you can do this independently of the Database. That's important if you use the new Attributes API to define (additional) attributes.
Getting all attributes from a model class:
pry> User.attribute_names
=> ["id",
"firstname",
"lastname",
"created_at",
"updated_at",
"email",...
Getting the type:
pry> User.type_for_attribute('email')
=> #<ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlString:0x007ffbab107698
@limit=255,
@precision=nil,
@scale=nil>
That's sometimes more information than needed. There's a convenience function that maps all these types down to a core set (:integer, :string etc.)
> User.type_for_attribute('email').type
=> :string
You can also get all that data in one call with attribute_types which returns a 'name': type
hash.
In rails 5 this will give you a list of all field names along with their data type:
Model_Name.attribute_names.each do |k| puts "#{k} = #{Model_Name.type_for_attribute(k).type}" end
This snippet will give you all the attributes of a model with the associated database data types in a hash. Just replace Post with your Active Record Model.
Post.attribute_names.map {|n| [n.to_sym,Post.type_for_attribute(n).type]}.to_h
Will return a hash like this.
=> {:id=>:integer, :title=>:string, :body=>:text, :created_at=>:datetime, :updated_at=>:datetime, :topic_id=>:integer, :user_id=>:integer}